Work on Rogers Stirk Harbour’s £135 million British Museum extension is set to begin next month after the controversial scheme was approved last night by Camden Council.

Members of the planning committee voted by nine to three to approve the reworked proposal, which was unexpectedly rejected over the summer.

A report by planning officers had urged planning permission be granted.

The original scheme involved three five-storey glass pavilions, with three basement levels, to provide space for a new exhibition gallery as well as conservation laboratories, offices and collection storage rooms.

The new plans reduced the building to two pavilions, which are slimmer and lower than originally planned with enlarged basements in order to add the necessary space lost above ground.

A spokeswoman for museum trustees hailed the go-ahead and thanked supporters including English Heritage.

"The building will ensure the British Museum can meet its fundamental obligations of preserving, researching, displaying and lending this unparalleled collection for future generations," she said. "The building will ensure the British Museum remains one of the world's leading museums, a civic space serving a local, national and international audience."

About £92 million has been raised towards the cost of the project, which was supported by English Heritage, Cabe and the Victorian Society but opposed by the Ancient Monuments Society, Georgian Group, Camden Civic Society and Twentieth Century Society.